Systemic lupus erythematosus (SLE) is a systemic immune complex disease of humans that affects multiple organ systems. The disease is characterized by rashes, arthritis, lung disease, and kidney disease. It occurs mostly in women and usually strikes during young adulthood. Perhaps the most severely affected organ is the kidney, and glomerulonephritis is the major cause of morbidity and mortality in patients with SLE. The current standard treatment for lupus nephritis is the alkylating agent cyclophosphamide, a strong immunosuppressive drug. Although treatment is generally effective, the drug has many side effects including infections, sterility, hair loss, and malignancy.
A wide variety of agents have been used to treat SLE. These agents may act either by interfering with collaborations between B and T lymphocytes, directly eliminating effector cells, or by blocking individual cytokines. Biological agents have had various levels of success in treating animal models of SLE. However, most agents require repeated treatment with high concentrations of mAb or protein antagonists.
The most commonly studied animal model of human SLE is the NZB X NZW F1 female mouse (NZB/W). This mouse shares many features with the human disease including severe proliferative glomerulonephritis, which is the major cause of death in the mice. The mice have high levels of circulating immune complexes (IC), which interact with Fc gamma receptors (FcR) in the kidney to induce nephritis. A second mouse model of human SLE is the MRL-Fas/pr mouse, which exhibits a more rapid progression of disease than the NZB/W mouse.
The innate immune system plays an important role in autoimmunity. One way in which the innate immune system molecules may affect autoimmunity is through the recognition and clearance of autoantigens released from apoptotic or necrotic cells. Other possible mechanisms for protecting against autoimmune-mediated inflammation include altering the cytokine response to inflammatory stimuli and by redirecting the adaptive immune system.
C-reactive protein (CRP) is the prototypic acute phase reactant in man and a component of the innate immune system. CRP binds to nuclear antigens that are the target of the autoantibodies of patients with SLE as well as to damaged membranes and microbial antigens. CRP activates the classical complement pathway and interacts with phagocytic cells through FcR. CRP is protective against various inflammatory states including endotoxin shock and inflammatory alveolitis. CRP protection against endotoxin shock requires FcR and is associated with FcR-dependent induction of interlukin-10 (IL-10) synthesis by macrophages.
It has been reported that CRP was protective against the accelerated disease in NZB/W mice injected with chromatin. It has also been demonstrated that NZB/W mice transgenic for human CRP had a delayed onset of proteinuria and enhanced survival. The ability of CRP to prolong survival in NZB/W mice has been attributed to increased binding and clearance of autoantigens or immune complexes. However, the ability of CRP to regulate acute inflammation suggests an alternative mechanism for its beneficial effects in SLE.
What is needed is an effective treatment for kidney disease (including that caused by SLE) that does not have the serious side effects attendant with cyclophosphamide treatment. What is also needed is an effective way to modify the response to autoantigens and thereby delay or even reverse nephritis caused by, for example, SLE.